Orbiting vacuum pump power supply with a filament current regulator



Oct. 10, 1967 D. P. SHELDON ORBITING VACUUM PUMP POWER SUPPLY WITH A FILAMENT CURRENT REGULATOR Filed Oct. 7, 1965 United States Patent 3,346,769 ORBITING VACUUM PUMP PGWER SUPPLY WITH A FILAMENT CURRENT REGULATOR Deane P. Sheldon, Franklin, Mass, assignor to National Research Corporation, Cambridge, Mass, a corporathin out Massachusetts Filed Oct. 7, 1965, Ser. No. 493,690

7 Claims. (Cl. 315-106) ABSTRACT OF THE DISCLOSURE The present invention relates to power supply circuitry for hot filament orbiting electron devices, such as vacuum pumps.

The principal object of the invention is to provide a power supply for orbiting electron devices which includes means for reversing the polarity of the direct current applied to the device and inexpensive overpressure control means for protecting the power supply in either setting of the polarity reversing means.

It is a further object and distinct advantage of this invention that the overpressure control means of the power supply are responsive to total current drawn by and produced within the device to give an indication of when the polarity of the device may be reversed from start to run conditions.

It is a further object of this invention that the power supply regulates filament current in response to variations in total current drawn by and produced within the orbiting electron device thereby maintaining total current in the device at a constant or a programmed level.

It is a further object of this invention to accomplish the foregoing with a simple, reliable, inexpensive circuit which provides protection against arcing within the device or at the terminals and provides such protection despite common operator errors.

The invention accordingly comprises the apparatus possessing the combination of elements and the arrangement of parts which are exemplified in the following detailed disclosure and the scope of application of which is indicated in the claims.

Reference is made to the accompanying drawings wherein:

FIG. 1 is a circuit diagram of the power supply according to a preferred embodiment of the invention with the polarity reversal switch in the run position; and

FIG. 2 is a portion of the FIG. 1 diagram with the polarity reversal switch in the starting position;

FIG. 3 is an improved embodiment of the filament current regulating circuit which is a component of the power supply of the present invention.

Structure The illustrated preferred embodiment comprises apparatus for supplying power from the conventional line supply of 117 volts, single phase alternating current, 50- 60 cycles per second to an orbiting electron vacuum pump 10. The pump, per se, is already known in the prior art and comprises a central electrode 12 with getter sources "ice 14 mounted thereon. The annular metal body 16 of the pump is grounded and serves as a second electrode. The orbiting electron vacuum pump is connected to a vacuum system 20 such as a coater or a furnace. Also included in the system are a roughing pump 22 with a valve 24 and a valve 26 for backfilling the evacuated system with air or an inert gas, as desired. In its cyclic operation, the system 20 is initially evacuated to a pressure of between 1 and microns by the pump 22. Then the power supply is connected to the central electrode 12 to make it highly negative (minus five to ten kilovolts, or larger, depending on pump size) with respect to the pump body 16. This causes a glow discharge to strike within pump 10 and the glow helps clean up the pump and has a pumping efiect which reduces the pressure to a level suitably low for starting the normal operation of the pump (about one to ten microns, depending on the pump). Once this requisite low pressure is reached, the operator throws a polarity reversing switch in the power supply so that electrode 12 becomes highly positive with respect to pump body 16. The operator also throws a filament on-off switch in the power supply to energize filaments 18 in the pump.

The power supply circuit comprises a rectifier 30 connected to the power input through a transformer 32 and an autotransformer 34. An indicator light 36 is connegted across the line terminals of the autotransformer. Between the power input and the autotransformer are circuit breaker switches 40' and 38'. Switch 38 is operated by solenoid 38 described below and switch 40' is interconnected to the polarity reversing switch 40 described below.

The filaments 18 are connected to autotransformer 34, the voltage input of which is adjusted by a transformer 50 through a series parallel switch 52. A filament indicator lamp 54 is connected across the primary terminals of transformer 50. A second rectifier 60* provides a source of reference voltage for an emission control circuit. The rectifier 60 is connected to a transformer 62, the voltage input of which is adjusted by autotransformer 64. A capacitor 66 and current comparison resistor 68 are provided in the control circuit. A saturable reactor 70' is connected between the filament energizing and control circuits. The filament bias circuit is connected to switch 52 via a bias adjusting resistor 56. A milliammeter 58, with a bypass capacitor 59, and a relay solenoid 38 are also provided in the emission control circuit.

The pump bias circuit, between polarity reversing switch 40 and pump 10, comprises load resistor 42, bleed resistors 44 and 46, and capacitor 48. The polarity reversing switch 40 is movable between a (pump) running position as shown in FIG. 1 and a start position as shown in FIG. 2. The switch 40 is connected to switch 42 so that power is cut off while the switch 49 is being moved between start and run positions to avoid arcing at the terminals of switch 40. The switch 40 is constructed so that it delays polarity reversal by at least one second (because the operator is obliged to make several mechanical motions) allowing capacitor 48 to discharge through the bleed resistors before the contact is remade.

Typically, the various circuit elements (related values) are selected as follows:

(a) Direct current circuit:

Autotransformer 345 ampere Powerstat (0 to v. A.C.). Transformer 32-9600 v. output 120 v. input. Bridge rectifier 3016,000 volts, peak inverse voltage per leg. Lamp 36-neon bulb. (b) Pump bias circuit:

Switch 40-See Fruzzetti, S.N. 483,719 filed Oct.

7, 1965. Resistor 4220K, 50 W. Resistor 44--10M.

Operation The sequence of a normal pumpdown cycle is that the roughing pump 22 is operated to bring the system down to a pressure on the order of 10 to 40 microns (valve 24 being open and valve 26 being closed). Then, with the polarity reversal switch 40 in its FIG. 2 start position, the operator turns on the power supply. In this position, the central electrode 12 is biased negatively with respect to the grounded annular electrode (pump body) 16. The autotransformer is turned up towards full power until a glow discharge is struck in the pump 10. This causes the meter 68 to indicate current flow. Whenever the reading of the meter runs the design value (e.g., O milliarnperes for a six-inch pump) the operator cuts back on the autotransformer 34 to hold the current down. The solenoid 38 is set to instantly open switch 38' if the current goes over 60 milliamperes.

After a period of about At hour to 2 hours, cleanup of the pump and weakening of the discharge will cause the current reading on meter 68 to drop. The operator then turns up the autotransformer 34 to increase the discharge and raise the reading of meter 58 back to 50 milliamps. After repeating this process several times, the operator will reach rated pump power on the transformer and the meter reading will be back to zero. At this point, the pump is ready for running.

The operator opens the main switch 33 and then throws polarity reversal switch 40 from its FIG. 2 start position to its FIG. 1 run position. If the operator forgets to out 01f power by Opening switch 33, the same result is accomplished by switch 42 which opens in response to movement of switch 40. After throwing switch 40 to the FIG. 1 position, the operator recloses switch 33 and closes switch 53 to heat the pump filaments. The pump power is adjusted to rated value through autotransformer 34. The filament heating current is adjusted through autotransformer 64 and the filament bias is adjusted via resistor 68.

After stable operation of pump is achieved, the operator cuts off pump 22 and closes valve 24.

During the running of the pump 10, the total current drawn by the pump comprises electron emission from the filaments 18 to the anode 12, occasional impact of electrons into the cathode 16, positive ion collection from the anode and secondary emission from the cathode. The principal component of this invention is the electron emission from the filament. Variations in total current are reflected in a change in Voltage drop across resistor 68, and in turn, by a change in voltage drop across the DC. windings of the reactor 70. A corresponding change is induced in the impedance of the AC. windings, thus changing the power input to the filaments 18. I have built several power supplies, as described herein, and have found that this arrangement provides a smooth,

4 stepless, control of total pump current and provide high efiiciency and pumping speed in operation of the pump 10.

Whenever an excessive current is generated in the power supply circuit, as by runaway discharge or arcing in the pump during starting or running conditions or by a short in the power supply circuit, then the instant trip relay 38 cuts off power to the pump bias circuit, the filament energizing circuit and the control circuit. This saves all components, except that in some instances the rectifier 68 may fail as the result of such an overload and the automatic regllation of emission function is lost. However, the operator may continue manual control of emission via autotransformer 64 since the mode of failure of rectifier 68 is by shorting through.

I have invented an improved form of emission control circuit which is particularly useful in the power supply circuit of FIG. 1 and a portion of which is shown in FIG. 3. The components of the improved emission control consist of:

A 500 ohm, 10 watt, resistor 162; two diodes each having a peak inverse voltage of 600 volts at one ampere; and two Zener diodes 161; each having a limiting voltage of 200 volts with a maximum tolerable surge current in excess of the rated current of the diodes 160 and a surge time tolerance in excess of the time required for tripping by relay 38.

In the particular circuit of FIG. 1, since the relay 38 requires milliseconds to operate, a particularly suitable Zener diode is the Unitrode UZ5210* which tolerates a maximum surge of 1.4 amperes for 8.3 milliseconds.

The components 62, 66, 70, 68, 38 are as in FIG. 1.

I have built the circuit of FIG. 1, including the improved emission control of FIG. 3. I have deliberately created shorts several times, putting 10,000 volts, positive, at the junction A in FIG. 3. In every instance, the relay 38 tripped and there was no failure of any of the diodes in the emission control circuit nor of any other portion of the power supply. Even if one of the diodes 160 should fail, the other diode 160 would continue to function and automatic regulation of emission would still be available.

Thus I have provided basic and improved forms of a power supply with self regulation and safety devices as described above without resort to choke coils, thyratrons, amplifier tubes and pressure gauges normally provided in power supply circuitry for devices of this character. Consequently, I am able to provide economy of size and cost and improved reliability of the power supply.

It will be obvious to those skilled in the art that the components of the power supply or emission regulator can be scaled up and down or replaced with structurally equivalent circuit arrangements. Also, while I have described the utility of my power supply particularly in connection with orbiting electron vacuum pumps, it will be apparent that the invention may be applied to other hot filament power tube devices where an equivalent control function is desired. It is therefore intended that the above description shall be read as illustrative and not in a limiting sense.

What is claimed is:

1. An improved power supply circuit for orbiting electron vacuum pumps, and the like, comprising in combination:

(a) a direct current source of high voltage,

(b) a pump bias circuit for connecting the said high voltage source to a first electrode of the pumpand comprising polarity reversal switch means,

(c) an alternating current source,

(d) a filament energizing circuit for connecting the said alternating current source to a thermionic emitting filament of said pump,

(e) a control circuit comprising a direct current source of a reference low voltage and a current sensing resistor, said current sensing resistor being located in series between the said polarity reversing switch and an electrode of said pump, and

(f) a saturable reactor with its alternating current windings in said filament energizing circuit and its direct current windings in said control circuit constructed and arranged so that increasing current drawn by said current sensing resistor is counteracted by decreasing filament heating power output and so that decreasing current drawn by said current sensing resistor is counteracted by increasing filament heating power output.

2. The power supply of claim 1 further comprising:

(g) an instant trip relay actuator located in series with said current sensing resistor and said pump electrode and constructed and arranged to cut 011? sources in 3. The power supply of claim 2 wherein the said sources in (a), (c), (e) draw power through a common adjustable power supply and are in parallel circuit rela-v tionship with each other, the direct current sources in (a) and (e) comprising solid state rectifiers.

4. An improved solid state control circuit for controlling a variable alternating current power supply for a filament or the like in response to variations in total current in the electric device incorporating the thermionic filament and comprising, in combination, an input transformer, a plurality of rectifier diodes, at least one Zener diode, a saturable core reactor and a current comparison resistor, and a control element for regulating power input to said filament and a current sensing resistor, the said components being arranged to form a series loop of the said secondary winding of said input transformer, said rectifier diodes, said control element and said current sensing resistor, said Zener diode being connected in parallel across the rectifier diodes and the secondary winding.

5. An orbiting electron vacuum pump with the power supply of claim 1 in combination therewith, the orbiting electron pump having a central anode electrode and annular cathode electrode and a filament for thermionically emitting electrons between said electrodes, the said electrodes being connected to the voltage source (a) via the pump bias circuit and control vircuit (e) and the said filament being connected to said filament energizing circuit (d)-at the end.

6. In an orbiting electron vacuum pump comprising a central anode electrode and an annular cathode electrode and a filament for thermionically emitting electrons between said electrodes, and a power supply for said pump comprising:

(a) a direct current source of high voltage,

(b) a pump bias circuit connecting the positive side of said voltage source to said anode,

(c) an alternating current source,

(d) a filament energizing circuit connecting said alternating current source to said filament,

(e) a control circuit comprising a direct current source of a referene low voltage and a current sensing resistor, said resistor being located in series between the negative side of said voltage source and the cathode electrode, and

(f) a saturable reactor with its alternating current windings in said filament energizing circuit and its direct current windings in said control circuit constructed and arranged so that increasing current drawn by said current sensing resistor is counteracted by decreasing filament heating power output and so that decreasing current drawn by said current sensing resistor is counteracted by increasing filament heating power output.

7. The pump of claim 6 wherein the said control circuit of the power supply (e) comprises an input transformer secondary winding, a plurality of rectifier diodes, a control winding of said reactor (f) and said current sensing resistor arranged in a series loop and also a Zener diode connected in parallel across the rectifier diode and the secondary winding.

References Cited UNITED STATES PATENTS 2,230,558 2/1941 Bowen 315-106 X 2,236,195 3/1941 McKessOn 315106 2,748,316 5/1956 Stevenson 315-406 3,078,388 2/1963 Hanks et a1. 315107 JAMES W. LAWRENCE, Primary Examiner.

C. R. CAMPBELL, Assistant Examiner. 

1. AN IMPROVED POWER SUPPLY CIRCUIT FOR ORBITING ELECTRON VACUUM PUMPS, AND THE LIKE, COMPRISING IN COMBINATION: (A) A DIRECT CURRENT SOURCE OF HIGH VOLTAGE, (B) A PUMP BIAS CIRCUIT FOR CONNECTING THE SAID HIGH VOLTAGE SOURCE TO A FIRST ELECTRODE OF THE PUMP AND COMPRISING POLARITY REVERSAL SWITCH MEANS, (C) AN ALTERNATING CURRENT SOURCE, (D) A FILAMENT ENERGIZING CIRCUIT FOR CONNECTING THE SAID ALTERNATING CURRENT SOURCE TO A THERMIONIC EMITTING FILAMENT OF SAID PUMP, (E) A CONTROL CIRCUIT COMPRISING A DIRECT CURRENT SOURCE OF A REFERENCE LOW VOLTAGE AND A CURRENT SENSING RESISTOR, SAID CURRENT SENSING RESISTOR BEING LOCATED IN SERIES BETWEEN THE SAID POLARITY REVERSING SWITCH AND AN ELECTRODE OF SAID PUMP, AND (F) A SATURABLE REACTOR WITH ITS ALTERNATING CURRENT WINDINGS IN SAID FILAMENT ENERGIZING CIRCUIT AND ITS DIRECT CURRENT WINDINGS IN SAID CONTROL CIRCUIT CONSTRUCTED AND ARRANGED SO THAT INCREASING CURRENT DRAWN BY SAID CURRENT SENSING RESISTOR IS COUNTERACTED BY DECREASING FILAMENT HEATING POWER OUTPUT AND SO THAT DECREASING CURRENT DRAWN BY SAID CURRENT SENSING RESISTOR IS COUNTERACTED BY INCREASING FILAMENT HEATING POWER OUTPUT. 